Process of solvent refining petroleum oils



Patented June 18, 1940 PATENT OFFICE PROCESS OF SOLVENT REFININGPETROLEUM OILS Arthur W. Hixson, Leonia, N. J., and Ralph Miller, NewYork, N. Y., assignors to The Chemical Foundation, Incorporated, acorporation of Delaware 'No Drawing. Application December 17, 1936,Serial No. 116,349

1 Claim.

This invention relates to the separation of petroleum oils intodifferent fractions, more particularly to the solvent fractionation ofoil by means of novel and highly selective solvents.

Crude petroleum oil is a complex mixture of different types or groups ofhydrocarbons. The respective percentages of these different hydrocarbongrou'ps vary considerably, depending upon the source or typeof thecrude. Thus, a typical as petroleum oil contains parafiinic, naphthenic,and

aromatic hydrocarbons, together with some asphalt. In certain crudes,such, for example, as the Pennsylvania crudes, the percentage of theparalfinic constituents is relatively very high and i115 the percentageof the naphthenic and aromatic constituents, commensurately low. On theother hand, certain other crude oils, such as Mid-Continent oils,contain a higher percentage of the naphthenic and aromatic constituentsand a com- 34 mensurately lower percentage of the paraffinichydrocarbons. The crudes are, therefore, broadly classified on thisdiiferential composition, being generally known as paraflin-base andasphaltic-base oils respectively.

The parafiinic constituents are saturated hydrocarbons having a very lowratio of specific gravity to distilling temperature. They are not actedon by concentrated sulphuric acid, are not nitrated by nitric acid and,comparatively; are 30 extremely resistant to all chemical reactions;

The naphthenic hydrocarbons are ring or cyclic compounds and arecommonly found in the heavier fractions of the crude petroleum oil.

These naphthenic constituents have a higher ra- 35 tio of specificgravity to distilling temperature than the parafiin compounds and arenot as resistant to chemical action as theparaflin compounds.

The aromatic or benzene hydrocarbons exist to m some extent in certainof the asphaltic base oils and are formed to a considerable degree inthe high temperature pyrogenetic conversion ofcrude stocks. Thesecompounds are more reactive than the paraffin hydrocarbons and are actedupon by strong mineral acids.

In cracked distillates other hydrocarbon constituents, such as theolefines, are present. These compounds contain less hydrogen and morecarbon than the parafiin hydrocarbons and are read-- 50 ily acted uponby sulphuric acid.

It is known that for most purposes the paraffinic base fractionsconstitute the best lubricants, especially for high temperaturelubrication, such as is required in internal .combustion engines.

a As more particularly pointed out in our copending application SerialNo. 60,634, patented Jan. 10, 1939, No. 2,143,415, the excellence of theparafiinic oils for lubricating purposes depends primarily upon theirrefractory character, their low volatility and their desirableviscosity-tempera- 5 ture characteristics.

It has been proposed heretofore to produce improved lubricating oils bysubjecting a complex hydrocarbon mixture of the character discussed tothe action of a solvent which has a selective afiinity for thenon-parafiinic constituents of the fraction being-treated. By the choiceof a proper solvent, it is theoretically possibleto preferentiallydissolve the naphthenic and aromatic constituents', to segregate thesolvent with its dissolved oil from the undissolved parafiinicconstituents and thus secure a fraction of high para'iiinicity.

Such a simple operation, however, has been difiicult of achievement.While a number of sin gle selective solvents have been proposed in thepast, such solvents do not, in fact, operate effectively. Thus, certainof these solvents, though highly selective, present but a low solubilityfor the non-parafiinic constituents, with the result that excessivelylarge amounts of the solvents must be employed, thus rendering the useof such a solvent commercially impractical. As more fully explained inour copending application, other factors impose limitations on the typeof single solvent which may be employed. Thus, an effective singlesolvent must not only possess a marked selectivity and satisfactorysolubility for the non-parafiinic hydrocarbons, but also must possesscertain other characteristics, such so as; a low melting point; arelatively low boiling point; a marked tendency to stratify from theparafiinic fraction at segregation temperatures;

a specific gravitysuiiiciently difierent from the paraifinic fraction toinsure rapid settling; a low solubility in Water, and rapidrecoverability by fractional distillation.

The difliculty in developing a single selective solvent whichsatisfactorily fulfills the established criteria has been so great thatthe solution of the problem has been sought by other methods. Thus ithas been proposed to achieve the desired fractionation by treating theoil stock with a mixture of solvents, such as the so-called dualsolvents. Methods have thus been proposed Which involve the use of anextraction medium comprising a mixture of primary and secondarysolvents, which solvents, per se, possess but little selectivity; butwhich, when used conjointly, do efiect some degree of selectiveextraction of-the 6! desired constituents. This type of procedure,obviously, is not as desirable as a single solvent extraction. Thus, theuse of dual solvents involves larger storage equipment, additional orspecially designed solvent recovery units, low operating temperatures,and similar factors which detract from the technical efiiciency andpractical economies of the operation.

As has been explained in our copending application Serial No. 60,634,patented Jan. 10, 1939, No. 2,143,415, markedly improved results areachieved by refining a mixed-base petroleum oil with a single polarsolvent which is characterized essentially by a high dipole moment. Aspointed out in that application, certain solvents of said type, such asortho-nitroanisole and ortho-methyoxybenzonitrile, present a strikingselectivity for the non-paraffinic constituents of the oil treated andpossess other physical and chemical characteristics which render thempeculiarly valuable for use.

In further experiments in this field we have discovered other solventsof this general type which are most effective for the selectivedissolution and removal of undesirable non-parafiinic constituents froma mixed-base oil. We have found that nitrile substituted heterocycliccompounds, as exemplified by furonitrile serve most effectively for thepurpose at hand.

This compound has proved to be an excellent selective solvent. It'sphysical characteristics, as will be appreciated, classify it as aselective solvent of optimum value. It has a boiling point of 146 C., at738 mm. and a density of 1.082, at 20 C.

To illustrate the peculiar efficacy of this solvent, equal weights offuronitrile and a Mid-Continent distillate were heated to above themiscibility temperature of 44 C. The resulting homogeneous liquid wascooled in a separatory apparatus with occasional agitation. On coolingbelow the miscibility temperature, the homogeneous liquid quicklyseparated into immiscible layers, a lower, dark-colored layer and alight, amber-colored, supernatant layer. The layers were separated at 25C., and each was subjected to vacuum distillation. Upon analysis it wasfound that the yield of rafiinate was 70% of the original oil, and theyield of extract was 30%. The oil layer contained 22% of the solvent,and the extractlayer contained 72.5%. Whereas the kinematic viscosityindex of the original oil was 55, the viscosity index of the raffinatewas 15.

It is particularly to be observed, as intimated hereinbefcre, that thephysical characteristics of this solvent render it particularlyeffective for the rapid and economical extraction of naphthenicfractions. The density is sufficiently great to insure rapid phaseseparation. This phase separation is accelerated to a considerabledegree because of the very satisfactory viscosity of the solvent, sinceit is of relatively high fluidity at the separation temperatures. Thisboiling point of 146 C. is such as to insure practical recovery of thesolvent with satisfactory thermal efficiency. In point of fact, thefuronitrile has a considerably lower boiling point than many of thewell-known solvents, such as phenol, nitrobenzene, aniline and the like.It presents the marked advantage of a relatively low miscibilitytemperature and one which is easily attained with a small expenditure ofcooling and heating media.

The particular example given to illustrate the effectiveness of theimproved solvent indicates the improved results to be obtained whenoperating under the best conditions. In the example, a batch method ofcontacting and agitation was chosen purposely to accentuate theeffectiveness of the material. When operating under improved conditions,such, for example, as continuous countercurrent extraction, improvedyields are attained and greater selectivity is secured.

Even under the conditions obtaining in the example given, the comparisonof the eificiency of furonitrile as a selective solvent with one of theWell known solvents, such as nitrobenzene, is striking. Thus, for thepurpose of establishing the comparative efficiency, similar extractionswere made utilizing nitrobenzene as the selective solvent. It was foundthat when an oil fraction of the type mentioned was extracted withnitrobenzene, to obtain a raflinate of equal quality, the yield was61.5% as compared to 70% for furonitrile. In the nitrobenzeneextraction, on the other hand, the percentage of solvent in thesolvent-layer was 75%, as against 72.5% in the furonitrilesolvent-layer. It is thus clearly evident that with furonitrile agreater yield is produced, even though the oil concentration in thefuronitrile solvent-layer was higher than in the correspondingnitrobenzene layer. This is a feature of special significance, since itclearly indicates that solutions of furonitrile, containing high oilconcentrations, retain their selectivity. In other words, as compared tonitrobenzene, smaller quantities of furonitrile are required per unitvolume of oil processed. Since the cost of solvent refining is largely afunction of the quantity of solvent used per volume of oil, reductionsin the quantity of solvent required are of paramount importance.

Another advantageous feature is the potentially low initial cost of thenew solvent. It may be made up, for example, from such cheap initialstarting material as oat hulls and the like. Such cheap material may betreated to produce furfural from which the furonitrile may be formed bysuitable methods.

It is clear then that compounds of the type of furonitrile present manyadvantages as a single selective solvent for solvent oil refining. Asnoted, it is characterized by a high selectivity, coupled with a mostsatisfactory yield. Its physical characteristics are such that it may beemployed at ordinary temperatures withoutthe use of expensiverefrigerating apparatus. It has a relatively low boiling point and,hence, may be volatilized and recovered with minimal expenditure ofheat. It is highly fluent under the operating conditions of the processand thus insures accelerated settling, even at the lower temperatures.In short, it combines, to a high degree, the desirable physical andphysicochemical characteristics of the optimum single selective solvent.1

It is also to be observed that furonitrile may be employed in animproved two-stage selective extraction process of the type disclosed inour copending application Serial No. 116,348. Furonitrile is aneffective selective solvent for oil and may be separated from theclarifying solvent, triamylamine, at approximately 21 C. Furonitrile maytherefore be employed in lieu of orthonitroanisole orortho-methoxy-benzonitrile for the process disclosed in said copendingapplication.

Selective solvent extractions of crude petroleum oils, distillates orpyrogenetic fractions, may be carried out, utilizing the improved typesof solvents herein defined, in a manner known to those skilled in theart. Such conditions as the oil outlet temperature and the solventoutlet temperature may be controlled, within relatively wide ranges, tocorrespondingly modify the quality and yield of rafiinate. It will beappreciated that, Whenever desirable, a two-stage operation may beconducted in which the raffinate produced in a preliminary extraction isretreated with the improved selective solvent, under the same orspecifically different temperature conditions, to further improve thecharacteristics of the paraffinic fraction.

It is to be understood that single solvents of the type defined hereinare especially valuable for the production of high viscosity indexparaffinic lubricating oil fractions. However, as will be appreciated,the principles of the invention may be utilized in any circumstanceswhere it is desired to separate the parafiinic from the nonparaifinicconstituents of any oil fraction in which such constituents originallyexisted. Therefore, while preferred modifications of the invention havebeen described, it is to be understood that these are given didacticallyto ilustrate the principles involved and not as limiting the inventionto the precise compounds and methods chosen for illustration.

We claim:

A process of refining petroleum oils which contain parafiinic andnon-parafiinic constituents which comprises contacting the oil withfuronitrile at temperatures above the miscibility temperature, coolingthe mass to stratify it into an oil phase and a solvent phase;separating the solvent phase with its dissolved oil from the oil phase,and treating such solvent phase with triamylamine under conditionsregulated to preferentially extract certain of the oil constituents fromthe iuronitrile phase.

ARTHUR W. HIXSON, RALPH MILLER.

